Stirling Generator guide

 Despite its apparent simplicity, there are a few difficult parts to make, such as the crankshaft, so long as you take your time and pay attention to detail, anyone can build this engine. No machine tools are required. It will probably take several days to build, depending on how many brews you have.

If you've never built a Stirling engine before, I strongly recommend building a smaller easier to build engine before embarking on this project. It's helpful to get a feel for how these engines works and how little friction there needs to be. This guide assumes you already know the basics of a Stirling engine. Small stirling engines can be hard to get running properly.

The displacer cylinder :

The displacer cylinder is made from a stainless steel water pasta container. It's about 95mm diameter and cut down to be around 235 mm tall. Stainless steel can hold up to intense heat, and will not corrode easily, so it is a good choice. It's not a good idea to substitute an aluminium container, the performance is abysmal compared to a stainless steel bottle.  Keep the lid from the pasta container, you'll need it for the diaphragm.

I bent some flanges around the top to allow it to be secured solidly to the wooden parts. I did this by cutting small incisions around 1 cm apart with tin snips and bending them over.

The cooling jacket:

The water jacket is made from some large 150 mm diameter tin cans. I spray painted them before assembly to help protect them from the water. To connect the water inlet.outlet I used two 15mm to 8mm brass couplings (ordinary plumbing parts). The 8mm nylon tubing can be fitted securely into these using compression olive, this is much stronger than my previous method of trying to epoxy them in place. The brass couplings are perhaps a little to big for this job, 8 mm - 8 mm couplings might have been better, but I couldn't get those at the time.

The displacer :

The displacer is made from stainless steel wire wool that is wrapped around a stainless steel mesh. The wool I used is described as fine stainless steel wool, but it's actually quite coarse. I haven't found anywhere in the UK where you can buy genuinely fine stainless steel wool.

Finished displacer

The wood top and bottom pieces :

This displacer is sandwiched between to pine boards. The flanges on the displacer cylinder secure it.

The diaphragm is secured using the lid from the pasta cylinder :

The crankshaft:

Run! This is the hardest most frustrating part of building the engine. It must be perfectly straight and have some fairly tight bends in it, it will probably take a long time to get this right. It's made from 4mm steel rod. You need to add the bearings and brass connectors as you make the crankshaft. I made a jig to help with forming the cranks.

The crankshaft supports.

The flywheel and magnet rotor

I had this steel disk cut by a company who do steel fabrication. It's 4mm thick and 170mm diameter. The magnet rotor/flywheel is current threaded onto the crankshaft. I cut a thread on the end of the crankshaft with a die. The magnets are held in place using only their own magnetism.

The diaphragm

The diaphragm is formed from a motorcycle inner tube. The rubber is heated until it starts to smoke, then it's pressed into shape and left overnight. In the morning it will have  taken the shape of the form (the pasta tin lid in this case).

The stator:

The stator contains 10 coils of 24 S.W.G enameled copper wire. I didn't count the turns, I just filled the coil former up to its limit. They all ended up pretty much the same weight and resistance. The coils are glued to a plywood disc, which will be screwed to the side of the engine.

The alternator is based around the bottom of a 150mm diameter tin can, so the stator outer circle is 195mm. This leaves just enough room for 10 40mm diameter coils. The coils have an inner diameter to match the 20mm diameter magnets

The stator backing plate.

Centre hole in the stator backing
Cutting a hole in the centre of the backing piece. This is to allow for the crankshaft and paste lids on the flywheel.

The coil form is made from two milk bottle lids with an M6 bolt through the centre. There are 5 20mm diameter penny washers to make the centre of the form. I use a paper slip around the washers to allow the coil to be released.

The coil former

Once the coil is wound fully, I fixed around the outside of the coil to help secure the wires.

Finished winding the coil.

Once all of the coils are finished, test them all to check they're all about the same resistance, and that there's no breaks in the wire.

Testing the resistance of the coils.

The finished coils can be epoxied down to the stator backing plate.

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